HAT-P-20b-HAT-P-23b: Four Massive Transiting Extrasolar Planets

Abstract

We report the discovery of four relatively massive (2–7 M J ) transiting extrasolar planets. HAT-P-20b orbits the moderately bright V = 11.339 K3 dwarf star GSC 1910-00239 on a circular orbit, with a period P = 2 . 875317 ± 0 . 000004 days, transit epoch T c = 2455080 . 92661 ± 0 . 00021 (BJD UTC ), and transit dura- tion 0 . 0770 ± 0 . 0008 days. The host star has a mass of 0 . 76 ± 0 . 03 M , radius of 0 . 69 ± 0 . 02 R , effective temperature 4595 ± 80 K, and metallicity [Fe / H] = +0 . 35 ± 0 . 08. The planetary companion has a mass of 7 . 246 ± 0 . 187 M J and a radius of 0 . 867 ± 0 . 033 R J yielding a mean density of 13 . 78 ± 1 . 50 g cm − 3 . HAT-P-21b orbits the V = 11.685 G3 dwarf star GSC 3013-01229 on an eccentric ( e = 0 . 228 ± 0 . 016) orbit, with a period P = 4 . 124481 ± 0 . 000007 days, transit epoch T c = 2454996 . 41312 ± 0 . 00069, and transit duration 0 . 1530 ± 0 . 0027 days. The host star has a mass of 0 . 95 ± 0 . 04 M , radius of 1 . 10 ± 0 . 08 R , effective temperature 5588 ± 80 K, and metallicity [Fe / H] = +0 . 01 ± 0 . 08. The planetary companion has a mass of 4 . 063 ± 0 . 161 M J and a radius of 1 . 024 ± 0 . 092 R J yielding a mean density of 4 . 68 +1 . 59 − 0 . 99 gcm − 3 . HAT-P-21b is a borderline ob- ject between the pM and pL class planets, and the transits occur near apastron. HAT-P-22b orbits the bright V = 9.732 G5 dwarf star HD 233731 on a circular orbit, with a period P = 3 . 212220 ± 0 . 000009 days, transit epoch T c = 2454930 . 22001 ± 0 . 00025, and transit duration 0 . 1196 ± 0 . 0014 days. The host star has a mass of 0 . 92 ± 0 . 03 M , radius of 1 . 04 ± 0 . 04 R , effective temperature 5302 ± 80 K, and metallicity [Fe / H] = +0 . 24 ± 0 . 08. The planet has a mass of 2 . 147 ± 0 . 061 M J and a compact radius of 1 . 080 ± 0 . 058 R J yielding a mean density of 2 . 11 +0 . 40 − 0 . 29 gcm − 3 . The host star also harbors an M-dwarf companion at a wide separation. Finally, HAT-P-23b orbits the V = 12.432 G0 dwarf star GSC 1632-01396 on a close to circular orbit, with a period P = 1 . 212884 ± 0 . 000002 days, transit epoch T c = 2454852 . 26464 ± 0 . 00018, and transit duration 0 . 0908 ± 0 . 0007 days. The host star has a mass of 1 . 13 ± 0 . 04 M , radius of 1 . 20 ± 0 . 07 R , effective temperature 5905 ± 80 K, and metallicity [Fe / H] = +0 . 15 ± 0 . 04. The planetary companion has a mass of 2 . 090 ± 0 . 111 M J and a radius of 1 . 368 ± 0 . 090 R J yielding a mean density of 1 . 01 ± 0 . 18 g cm − 3 . HAT-P-23b is an inflated and massive hot Jupiter on a very short period orbit, and has one of the shortest characteristic infall times (7 . 5 +2 . 9 − 1 . 8 Myr) before it gets engulfed by the star.